Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Wafer level chip scale module packages (WLCSMP) and fan-out wafer level chip scale packages (FO-WLCSP) typically contain stacked semiconductor die over and between an organic substrate or interposer for higher device integration. Examples of the WLCSMPs with upper and lower stacked semiconductor die can be found in U.S. Pat. Nos. 6,921,968, 5,977,640, and 6,906,415. The lower semiconductor die is thinner than the organic substrate and thus contained within the encapsulant. Accordingly, it is difficult to properly dissipate heat from the lower semiconductor. The fixed organic substrate requires care when handling to avoid damage to the thin semiconductor die. In addition, warpage is a recurring issue due to mismatches in the coefficient of thermal expansion (CTE) between the upper and lower semiconductor die and organic substrate.
In FO-WLCSP, the bumps on the upper semiconductor die are typically large in diameter with a corresponding high pitch. The large pitch of upper die bumps limits the ability to mount a fine-pitch die with high input/output (I/O) count. In addition, the bump collapse for large balls is difficult to control, particularly when mounted on adhesive tape or carrier. The bump collapse increases chances of electrical shorting to adjacent conductive structures during reflow. The lower semiconductor die is prone to shifting during encapsulation due to inadequate adhesion between die and carrier.